Fatherhood: the benefits of leaving it late

A study shows older fathers are more likely to pass on genetic mutations. But we make up for it in our ability to nurture

'Looking at the entire task of fatherhood, if one compares the suitability of a 20-year-old to a 40-year-old, the younger man has few advantages'. Photograph: Jupiterimages/Getty
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No man over the age of 40 who has ever had the misfortune to glance in a mirror will be surprised to hear that his sperm quality is not what it once was. You don't need a PhD in genetics to figure out that in biological terms you have long since peaked.

Scientists at deCODE genetics in Iceland, however, have quantified an aspect of this decline in a new way. A 40-year-old father, it has been revealed, is approximately twice as likely to conceive a child with autism or schizophrenia as a man half his age. With all the speed of a nugget of juicy celebrity gossip, this story has spread across the world from the pages of science journal Nature.

Women are already familiar with this narrative. Reared in societies which expect them to achieve financial independence and career success, they are often at the same time criticised and mocked for delaying parenthood until their late 30s. Caught between the rock of science and the hard place of social expectation, the modern woman cannot win. Men can now be beaten with the same stick. Biologically speaking, it would appear that both men and women should be producing children a good decade before most of us actually do it.

The biological clock will always tick louder for women than for men, not least because the age at which men stop reproducing is a matter of choice and circumstance rather than biological determinism. While many childless women in their late 30s and early 40s agonise over their declining fertility, men will never feel a definitive cut-off date looming ahead of them. Rupert Murdoch had a child at 72, Saul Bellow at 84, Les Colley, an Australian miner, at 92.

While only a minority of men are likely to think it is a good idea to continue having children beyond retirement age, this study opens up to men a question that perhaps has never troubled them before. Is it selfish to delay reproduction until it is convenient, knowing that your child's health may be adversely affected by this choice? All older mothers have faced up to this question and reached a conclusion that suits them. Now it appears men should think about it, too.

The science, however, only gets you so far. Looking at the entire task of fatherhood, if one compares the suitability of a 20-year-old to a 40-year-old, the younger man has few advantages. As we age, our spermatozoa mutating away inside us, we also become calmer, more patient, less obsessed with personal ambitions, our lifestyles less frenetic. One of the great ironies of masculinity is that our physical decline, our gradual diminishing of virility, is what brings out the qualities likely to turn us into good fathers.

As someone aged 41 who has just had a third child, I know I am a much better father now than I was nine years ago, when I had my first. We older fathers may be passing on slightly lower quality genetic material, but where it really counts, in the area of nurture, fortysomethings are likely to do a far better job than twentysomethings.

There is also the environment to consider. A more significant factor in population increase than the number of children you have is the age at which you have them. A society of young parents will grow in number faster than one of older parents. If I were to have followed the geneticists' advice for optimum reproduction, my son would not be at primary school, he'd be at the maternity ward with his pregnant wife. On an overpopulated planet, late parenthood benefits everyone.

Not too late, of course. Rupert, Saul and Les should probably have known better. But we must remember that the genetic material we pass on is only a small fraction of the job of a father. If you are too young to give yourself up to the needs of your children, you are too young to be a parent.